Percussion bits

ABSTRACT

A percussion bit used in air hammer apparatus. The bit has a substantially flat, lower face in its main body portion from which compressed air discharges from bit passages to sweep formation cuttings or chips towards the sides of the bit body and upwardly around the exterior of the body. A multiplicity of tungsten carbide, or similar, buttons comprising rear or shank portions are embedded in the body, with tapered forward portions projecting substantially from the bit face for indenting and impacting upon the bottom of the bore hole being drilled in the formation, the forward portions of each button protruding from the bit face more than about 0.7 the diameter of its shank portion, whereby larger formation cuttings or chips are produced in the bottom of the bore hole, the bit drilling at a faster rate.

United States Patent 1191 Curington 1 1 PERCUSSION BITS v [75] Inventor: Alfred R. Curington, Houston, Tex.

[73] Assignee: Baker Oil Tools, Inc., Los Angeles,

Calif.

[22] Filed: May 8,1972

[21] Appl. No.: 251,212

[52] US. Cl.. 175/410, 175/418 [51] Int. Cl. ..E21c 13/08, E2lc 13/01 [58] Field of Search.. 175/409, 410, 414418 [56] References Cited UNITED STATES PATENTS 3,536,150 10/1970 Stebley 175/410 X 3,071,201 l/l963 Phipps 175/410 3,185,228 5/1965 Kelly 175/418 X 2,725,216 11/1955 Brown 1. 175/417 X 3,269,470 8/1966 Kelly 1 175/415 X 3,346,060 10/1967 Beyer 175/410 3,357,507 12/1967 Stewart 1 175/418 X 3,388,756 6/1968 Varel et a1 175/418 3,522,852 8/1970 Bardwell 175/410 X Jan. 29, 1974 3,693,736 9/1972 Gardner 175/410 Primary Examiner-David H. Brown Attorney, Agent, or FirmBernard Kriegel 571 ABSTRACT A percussion bit used in air hammer apparatus. The bit has a substantially flat, lower face in its main body portion from which compressed air discharges from bit passages to sweep formation cuttings or chips towards the sides of the bit body and upwardly around the exterior of the body. A multiplicity of tungsten carbide, or similar, buttons comprising rear or shank portions are embedded in the'body, with tapered forward portions projecting substantially from the bit face for indenting and impacting upon the bottom of the bore hole being drilled in the formation, the forward portions of each button protruding from the bit face more than about 0.7 the diameter of its shank portion, whereby larger formation cuttings or chips are produced in the bottom of the bore hole, the bit drilling at a faster rate.

12 Claims, 12 Drawing Figures PERCUSSION BITS The present invention relates to percussion bits for use in air hammers containing a hammer piston reciprocable for repeated impacting against the bit to penetrate its cutting elements into the formation being drilled.

In the drilling of bore holes in relatively hard formation, percussion bits are employed. A hammer piston is reciprocable by compressed air for repeated impacting against the bit to penetrate its cutting elements into the formation while the air hammer and bit are rotated, so

that the cutting elements cover substantially the full area of the bottom of the bore hole being drilled, the compressed air exhausting against the bottom of the bore hole to sweep the cuttings from the cutting region and upwardly around the bit toward the top of the bore hole. Prior bits used in air hammers have tungsten carbide, or similar, buttons projecting from the lower face of the bit body for impacting against the bottom of the bore hole being drilled, while air is discharged from the bit for removing the cuttings or chips from the bottom of the hole. Some bits have a flat bottom face from which the carbide buttons project. However, the bit face becomes severely battered during use which is believed to be due to the fact that such face impacts against the cushion of cuttings or chips remaining on the bottom of the hole, due to the inability of the exhausting air to remove them rapidly from the drilling area. In fact, some of the exhaust passages or nozzles on the bits are directed in such manner that the compressed air issuing therefrom actually impedes flow of the chips from the bottom of the bore hole. The protrusion of the buttons from the bit face is limited, or of relatively small extent, and the buttons themselves are of a comparatively small size, the clearance between the bit face and the bottom of the bore hole necessarily being limited. Such limited protrusion lowers the extent of indentation or penetration of the buttons into the hole bottom, and causes the severe battering action on such face. A greater extent of button protrusion cannot be effected since the buttons would break. A further disadvantage of prior percussion or hammer bits is the fact that there is very little clearance between the main body of the bit immediately behind the gauge buttons and the inner wall of the bore hole being produced. This requires that all chips produced must pass through vertical chip slots provided in the outer portion of the bit body, such slots being relatively small. The gauge buttons on the prior bits also have a larger area of contact against the wall of the hole, which offers resistance to downward movement of the bit under the action of the hammer piston, wear on such gauge buttons also resulting in the loss of gauge holding ability of the bit.

By virtue of the present invention, a pneumatic or hammer bit is provided that produces larger chips as a result of its impacting or indenting against the bottom of the hard formation, in which the cuttings are swept rapidly from the bottom of the hole and are capable of passing more readily around the outer portion of the bit body for upward conveyance by the air to the top of the bore hole, resulting in a faster drilling rate of the bit and a longer bit life. More specifically, the buttons protrude to a much greater'extent than heretofore from the lower face of the bit body, providing for increased penetration of the buttons into the formation, as well as a greater space and passage area between the bit face and hole bottom through which the air can sweep the cuttings from the bottom of the hole. This larger elevation of the bottom face of the bit body from the hole bottom also prevents such face from being caused to impact upon previously formed chips resting on the bottom. The cuttings are caused to flow past the exterior of the bit body by providing a greater side clearance with the inside diameter of the bore hole, also resulting in less grinding of the cuttings between the body of the bit and the wall of the hole. The gauge carbide buttons also have less contact with the wall of the hole, reducing resistance to transmission of the downward impacting force of the hammer piston through the bit, and driving of the bit buttons into the formation. Not only can the chips or cuttings flow more readily around and upwardly through the space between the bit body and the wall of the bore hole, but they can also pass through vertical grooves or slots provided in the exterior of the bit body.

This invention possesses many other advantages, and

has other purposes which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specification; These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is a longitudinal section through an impact bit embodying the invention disposed in the lower portion of an air hammer apparatus;

FIG. 2 is a cross-section taken along the line 2-2 on FIG. 1;

FIG. 3 is a bottom plan view of the drill bit disposed in a bore hole, taken along the line 3-3 on FIG. 1;

FIG. 4 is a fragmentary longitudinal section taken along the line 4-4 on FIG. 3;

FIG. 5 is a fragmentary longitudinal section taken along the line 5-5 on FIG. 3;

FIG. 6 is a longitudinal section taken along the line 6-6 on FIG. 3;

FIG. 7 is an enlarged fragmentary section through the reamer or gauge portion of the bit illustrated in FIGS. 1 and 3;

FIG. 8 is an enlarged fragmentary section through another portion of the bit illustrated in FIGS. 1 and 3;

FIG. 9 is a bottom plan view, similar to FIG. 3, of a modified form of a drill bit;

FIG. 10 is a longitudinal section taken along the line 10-10 on FIG. 9;

FIG. 11 is a longitudinal section taken along the line 11-11 on FIG. 9; and

FIG. 12 is a longitudinal section taken along the line 12-12 on FIG. 9.

In FIG. 1, the lower portion of a bore hole air hammer apparatus A is illustrated as representative of one specific form of apparatus that can be used in effecting repeated impact blows against a percussion bit 10 extending into its lower portion. A complete specific apparatus is disclosed in United States of America patent application for Bore Hole Air Hammer, Ser. No. 246,837, filed Apr. 24, 1972. As described in such application, compressed air passes downwardly through a string of drill pipe (not shown) secured to a housing 1 l of the apparatus, and is caused to be directed alternately to the upper and lower ends of a hammer piston tent, another pair of buttons 14d is disposed on opposite sides of the bit axis to a greater radial extent than the buttons 14c, while four buttons l4e are disposed in circumferentially spaced relation to each other to yet E of the bore hole F being produced, while the drill 7 string and housing 11 are rotated to rotate the bit 10.

The air exhausting from the housing is caused to pass downwardly through a central air or fluid passage 16 extending downwardly from the upper end of the anvil or shank portion 13 of the bit, such central passage communicating with one or a plurality of air exhaust or nozzle passages 17 opening through the lower bit face 18 at the bottom of the main bit body 20. The air discharging from the ,bit face sweeps the cuttings below the bit body in a lateral outward direction toward the wall F of the bore hole being drilled, carrying them upwardly around the bit body 20 and through the annular space 19 between the wall of the bore hole and the housing and drill string to the top of the bore hole.

As disclosed and described in the above-identified application, the rotation of the anvil bit is effected while drilling weight is being imposed upon the bit by the drill string bearing against the housing 1 l, and causing the lower portion 21 of the housing structure to bear against an upwardly facing transverse shoulder 22 on the bit body 20, the rotary drive being transferred from the housing structure to the anvil through a suitable spline type of connection. As illustrated, the specific drive connection includes circumferentially spaced elongatechordal surfaces 23 in the upper portion of the anvil 13, which are preferably concave in shape, against which correspondingly shaped segments 24 bear, these segments being carried in circumferentially spaced windows 25 in a drive member or housing head 26 forming the lower portion of the housing. The chordal surfaces 23 are substantially longer than the length of the segments 24, permitting relative longitudinal movement of the anvil bit with respect to the housing structure 11. The rotary effort is transferred from the housing section 11 to the drive member 26 by virtue of a threaded connection 27, and from the sides of the circumferentially spaced windows or openings 25 to the segments, from where the turning effort is transmitted through the abuttingsegments 24 and anvil surfaces 23 to the anvil bit 13. l

The reciprocating hammer piston 12 repeatedly impacts against the upper end 28 of the anvil bit, driving the buttons 14, embedded in the bit body 20, and which project from the bit face 18, against the bottom E of the bore hole and indenting or penetrating them the bore hole being drilled. The carbide or equivalent buttons or cutting elements 14, 15 are disposed in spaced relation to one another (FIG. 3), so as to collectively cover substantially the full area of the bottom E of the bore hole during the rotation of the bit and the impacting action transmitted from the piston 12 through the anvil bit 10 to the formation.

As disclosed most clearly in FIG. 3, a single button 14a is disposed adjacent to the axis 30 of the bit, a second cutter 14b is disposed a greater radial distance from the bit axis, a pair of buttons 146 is disposed on opposite sides of the bit axisto a still greater radial exa further radial extent from the bit axis 30. Finally, a number of reaming or gauge buttons 15 is disposed in circumferentially spaced relation to each other to a greater radial extent than all of the other buttons for impacting against the bottom E of the bore hole adjacent to its wall F, and also for action upon the wall itself, to produce the bore hole to the required diameter. The gauge buttons 15 have axes 31 (FIGS. 6, 7) inclined downwardly and outwardly with respect to the axis of the bit, the forward portion 15a, 15b of each gauge button being adapted to impact against the bottom of the bore hole adjacent to its side wall, as well as against the side wall itself, in order to maintain the bore hole to gauge.

The air exhausting from the bit discharges from the bit passages .17 in an inclined outward direction, as to sweep in a lateral outward direction toward the perimeter 32 of the bit body, and in an unimpeded manner, so

as to sweep all cuttings from the space 33 between the bit face 18 and the bottom E of the bore hole toward the wall F of the bore hole, and upwardly around the perimeter 32 of the bit into the annular space 19 between the housing 11 and the wall of the hole. In this connection, it is to be noted that the perimeter 32 of the lower portion of the bit body adjacent to the gauge buttons or cutters 15 is of a substantially lesser diameter than the diameter of the bore hole F, to provide substantial clearance through which the cuttings can be carried by the air in an upward direction.

The bit body also has relatively deep vertical external grooves 34 extending upwardly from the bit face 18 through which relatively large formation chips produced by the buttons can flow more readily into the larger annular space 19a between the upper portion of the bit body 20 below the shoulder 22, these relatively deeper grooves 34 being disposed on substantially diametrically opposite sides of the body. Between the deep grooves, the body has shallower vertical external grooves 35 between the gauge buttons 15 and extending from the bottom 18 of the. bit body to the upper portion of the bit body, where the annular space 19a between the bit body and the wall of the hole is greater than the lower portion for the reception of smaller chips or cuttings.

The discharge of the exhaust, air through the passages 16, 17 and their outward sweep laterally across the bottom E of the bore hole, coupled with the substantial side clearance or annular space 19b between the bottom portion of the=bit body and the wall F of the bore hole, as well as the provision of the relatively deep vertical grooves 34 and shallow vertical grooves 35, result in a greatly increased and rapid removal of the cuttings from the bottom E of the hole, enabling the buttons 14, 15 to impact against a relatively clear hole bottom. This action is to be contrasted with their impacting against a bed of cuttings or chips remaining on the hole bottom when prior bits are used. The result is a greater penetration of the forward portions l4r, 14s and 15a, 15b of the buttons into the bore hole formation. As explained hereinbelow, such greater penetration and increased removal of the cuttings from the bottom E of the bore hole is further enhanced by the greater vertical clearance space P provided between the bit face 18 and the bottom E of the bore hole, as a result of the greater protrusion of the buttons from the bottom face of the bit.

As disclosed in the drawings, the gauge buttons are inclined in a downward and outward direction. The other buttons 14 have their axes 45 substantially parallel to the axis 30 of the bit l0. Each of such buttons 14 includes a rear portion or shank 50, preferably of cylindrical shape, having a press-fit in a companion socket 51 provided in the bit body 20, the inner end 52 of the shank bottoming against the base 53 of the socket. Each of such buttons 14 also includes a forward portion 14r,14s, illustrated as being specifically of double conical form, extending in a downward direction from the cylindrical shank, the lower portion 50a of the shank projecting below the bitface 18. The conical portion includes a rearward cone 14s making a particular angle V with the axis 45 of the button, this rearward cone merging into a smaller forward cone l4r, the side of which makes a particular angle W with the axis 45 of the button. As an example, the angle V that the tapered side of the rearward or major cone 14s makes with the button axis 45 may vary from about 25 to 35; whereas, the angle W that the forward minor cone 14r makes with the shank axis 45 may vary from about 55 to 65. By way of specific example, the angle V that the tapered side of the major cone 143 makes to the shank axis 45 can be 30; whereas, the angle W that the tapered side of the minor cone l4r makes to the shank axis 45 may be 60.

The extent of protrusion P of the button 14 below the bit face 18 is greater than about 0.7 times the diameter D of the button shank 50. Such extent of protrusion, although greater than that found in prior bit arrangements, still results in a button of sufficient strength to withstand the impacting action transmitted by the hammer piston 12 through the bit 10 and its buttons to the bottom E of the bore hole. At the same time, it results in the greater. clearance or standoff P of the bit face 18 from thebottom E of the bore hole, providing the greater clearnace noted above through which air can sweep the cuttings from the bottom of the bore hole,

while causing the bit face 18 to remain above the cuttings that might be present on the hole bottom, so as to avoid the battering action of the bit face against a mass of cuttings, as in prior bits. In a preferred bit, the extent of protrusion P has been about 0.8 times the shank diameter D. Y

The major and minor cones 15b, 15a of the gauge buttons 15 are essentially the same as the buttons 14 above described, as well as the extent of their protrusion P from the outer tapered surface 18a of the bit body. The forward portions 15a, 15b of such buttons project laterally to a substantial extent beyond the lower periphery of the bit body 20 at its lower portion (FIG. 7), furnishing a greater clearance between the perimeter 32 of the bit body and the wall F of the well bore through which smaller chips can pass more readily, larger chips moving upwardly through the shallow vertical grooves 35 and the much deeper vertical grooves 34 in the bit body. It will be noted that the tapered exterior of the forward or minor cone 15a of each gauge button 15 engages the bottom E of the bore hole, as well as the lower portion F1 of the side wall F of the bore hole, which tapers slightly in a downward direction. However, the conical surface of the major or rearward cone 15b makes an angle X to the axis 31 of the shank 50 of the gauge button, such that the conical surface does not engage the wall F of the bore hole. As a result of the conical surface of the major cone being out of engagement with the wall of the hole, there is lesser resistance offered to penetration of all of the bit buttons 14, 15 into the formation, greater impact energy being imparted through the buttons to the bottom E of the bore hole, to produce cuttings or chips. The major cone 15b makes an angle X of from about 25 to 35 to the axis 31 of the shank, which is the same angle that the major cone 14s of each button 14 make to the axis 45 of its button shank 50. However, the axis 31 of each gauge button shank 50 makes an angle Y to the wall F of the bore hole, which is the same angle that it makes to the axis 30 of the bit 10, of from about 30 to 40, always being greater than the angle X that the major cone 15b makes to the axis 31 of the gauge bit shank. This results in a downward and laterally outward inclination of the outermost portion of the major cone 15b of the gauge button to the wall F of the bore hole,

preventing its surface contact therewith, and thereby minimizing the resistance to impact referred to above. In a specific design, the angle Y between the inclined axis 31 of the gauge button 15 and the wall F of the bore hole, or bit axis 30, is about 35, the angle that the major cone side makes to the shank axis being about 30, as noted above.

In the specific form of bit illustrated in FIGS. 9 to 12, the general relationship of parts described above applies, including the extent of protrusion .P of the buttons 14, 15 from the bottom face 18 of the bit and from the tapered reamer portion 18a of the bit body 20. However, the buttons 14a, 14b closer to the axis 30 of the bit may have a smaller diameter than the other buttons; whereas, some of the buttons 142 in the outer portion of the bit may also be inclined to the bit axis 30 but at a steeper angle of inclination than the gauge buttons 15. The exterior side of the bit body 20 has a much deeper groove 34a between a pair of gauge buttons 15 that permits freedom of passage of large chips or cuttings upwardly therethrough, there being substantially shallower vertical grooves 340 in the body, circumferentially spaced from one another, through which comparatively small chips can move, and a pair of circumferentially spaced intermediate depth vertical grooves 35b in the side of the bit body remote from the groove 34 a of maximum depth.

It is found that bits embodying applicants invention have a substantially greater life than prior bits, the drilling rate of the bit being substantially increased. In addition, the life of the bit can be still further increased by reshaping the buttons 14, 15 of a worn bit to improve its drilling rate by use of a'small grinder. The greater protrusion P of the buttons from the face of the bit enables this to occur. Reshaped bits having double conical buttons of common design wear to a substantially hemispherical shape, which does not have the formation penetration ability of a button in which the foward penetrating portion makes a steeper angle to the bottom E of the bore hole. With applicants arrangement, a driller can use a small grinder to reshape the worn buttons. There is sufficient protrusion P for such reshaping to be made to a somewhat parabolic form which provides a more desirable button indenter for impacting against and penetrating into the bottom E of the bore hole. Moreover, such parabolic form can be accomplished with less grinding. Actually, a new button with a parabolic form would also be desirable for use, but it is easier and more economical to produce from carbide material new buttons with the double forward and rearward cones 14r, 14s and 15a, 15b.

I claim: I

1. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; the forward portion of each button projecting downwardly below said drilling face more than about 0.7 times the-diameter of the rear shank portion of such button; the forward portion of each button including a major conical portion tapering downwardly from said rear shank portion and a minor conical portion tapering downwardly from said major portion.

2. In a percussion bit as defined in claim 1; the tapered surface of said major conical portion being inclined to the axis of said button from about 25 to 35, the tapered surface of said minor conical portion being inclined to the axis of said button from about 55 to 65.

3. In a percussion bit as defined in claim 1; and air passage means extending through said body from its upper end to discharge all air flowing into said passage means downwardly toward the bottom of the bore hole and laterally outwardly toward the perimeter of said body to sweep formation chips produced by said buttons from the spacebetween said drilling face and bottom of the bore hole.

j 4. In a percussion bit as defined in claim 1; said bottoindrilling face lying in a single plane extending from the axis of the bit body and laterally to the region of the perimeter of the bit body; the tapered surface of said major conical portion being inclined to the axis of said button from about 25 to 35, the tapered surface of said minor conical portion being inclined to the axis of said button from about 55 to 65.

5. In a percussion bit as defined in claim 1; said bottom drilling face lying in a single plane extending from the axis of the bit body and laterally to the region of the perimeter of the bit body; the tapered surface of said major conical portion being inclined to the axis of said button from about 25 to 35, the tapered surface of said minor conical portion being inclined to the axis of said button from about 5 to 65; said body having external circumferentially spaced vertical grooves extending upwardly from the bottom drilling face and through which formation chips can be carried upwardly by the air from the hole bottom.

6. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during'repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face;- the forward portion of each button disposed inwardly of said gauge buttons projecting downwardly below said drilling face more than about 0.7 times the diameter of the rear shank portion of such button; each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of said body at a greaterangle than the tapered side of said major conical portion is-inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the-bore hole.

' 7. In a percussion bit as defined in claim 6; the axis of said gauge button being inclined to the axis of said body at an angle of from about 30 to 40, the tapered side of said major conical portion of said gauge button being inclined to the axis of said gauge button at an angle of from about 25 to 35.

8. In a percussion bit for drilling a borehole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; the forward portion of each button including a major conical portion tapering downwardly from said rear shank portion and a minor conical portion tapering downwardly from said major portion; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face, each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of the body at a greater angle than the tapered side of said major conical portion is inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the bore hole.

9. In a percussion bit as defined in claim 8; and air passage means extending through said body from its upper end to discharge all airflowing into said passage means downwardly toward the bottom of the bore hole and laterally outwardly toward the perimeter of said body to sweep formation chips produced by said buttons from the space between said drilling face and bottom of the bore hole.

10. In a percussion bit as defined in claim 9; said body having external circumferentially spaced vertical grooves extending upwardly from the bottom drilling face and through which the formation chips can be'carried upwardly by the air from the hole bottom.

1 1. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom ofthe bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face, each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of said body at a greater angle than the tapered side of said major conical portion is inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the bore hole.

12. In a percussion bit as defined in claim 11; the axis of said gauge button being inclined to the axis of said body at an angle of from about 30 to 40, the tapered side of said major conical portion of said gauge button being inclined to the axis of said gauge button at an angle of from about 25 to 35. 

1. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; the forward portion of each button projecting downwardly below said drilling face more than about 0.7 times the diameter of the rear shank portion of such button; the forward portion of each button including a major conical portion tapering downwardly from said rear shank portion and a minor conical portion tapering downwardly from said major portion.
 2. In a percussion bit as defined in claim 1; the tapered surface of said major conical portion being inclined to the axis of said button from about 25* to 35*, the tapered surface of said minor conical portion being inclined to the axis of said button from about 55* to 65*.
 3. In a percussion bit as defined in claim 1; and air passage means extending through said body from its upper end to discharge all air flowing into said passage means downwardly toward the bottom of the bore hole and laterally outwardly toward the perimeter of said body to sweep formation chips produced by said buttons from the space between said drilling face and bottom of the bore hole.
 4. In a percussion bit as defined in claim 1; said bottom drilling face lying in a single plane extending from the axis of the bit body and laterally to the region of the perimeter of the bit body; the tapered surface of said major conical portion being inclined to the axis of said button from about 25* to 35*, the tapered surface of said minor conical portion being inclined to the axis of said button from about 55* to 65*.
 5. In a percussion bit as defined in claim 1; said bottom drilling face lying in a single plane extending from the axis of the bit body and laterally to the region of the perimeter of the bit body; the tapered surface of said major conical portion being inclined to the axis of said button from about 25* to 35*, the tapered surface of said minor conical portion being inclined to the axis of said button from about 55* to 65*; said body having external circumferentially spaced vertical grooves extending upwardly from the bottom drilling face and through which formation chips can be carried upwardly by the air from the hole bottom.
 6. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face; the forward portion of each button disposed inwardly of said gauge buttons projecting downwardly below said drilling face more than about 0.7 times the diameter of the rear shank portion of such button; each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of said body at a greater angle than the tapered side of said major conical portion is inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the bore hole.
 7. In a percussion bit as defined in claim 6; the axis of said gauge button being inclined to the axis of said body at an angle of from about 30* to 40*, the tapered side of said major conical portion of said gauge button being inclined to the axis of said gauge button at an angle of from about 25* to 35*.
 8. In a percussion bit for drIlling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; the forward portion of each button including a major conical portion tapering downwardly from said rear shank portion and a minor conical portion tapering downwardly from said major portion; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face, each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of the body at a greater angle than the tapered side of said major conical portion is inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the bore hole.
 9. In a percussion bit as defined in claim 8; and air passage means extending through said body from its upper end to discharge all air flowing into said passage means downwardly toward the bottom of the bore hole and laterally outwardly toward the perimeter of said body to sweep formation chips produced by said buttons from the space between said drilling face and bottom of the bore hole.
 10. In a percussion bit as defined in claim 9; said body having external circumferentially spaced vertical grooves extending upwardly from the bottom drilling face and through which the formation chips can be carried upwardly by the air from the hole bottom.
 11. In a percussion bit for drilling a bore hole in a formation: a body having a bottom drilling face; individual cutting elements comprising buttons having rear shank portions secured to said body and forward portions projecting downwardly below said drilling face, said buttons being disposed in spaced relation to each other and being so arranged on said body as to collectively act upon substantially the full area of the bottom of the bore hole during repeated impacting action imparted to said body and buttons while said body and buttons are being rotated in the bore hole; said cutting elements including a row of circumferentially spaced gauge buttons inclined in a downward and laterally outward direction from said drilling face, each gauge button including a rear shank portion secured to said body and a forward portion projecting downwardly below said drilling face and laterally outwardly beyond the maximum perimeter of said body, the forward portion of each gauge button including a major conical portion tapering downwardly from its rear shank portion and a minor conical portion tapering downwardly from said major portion, the axis of said gauge button being inclined to the axis of said body at a greater angle than the tapered side of said major conical portion is inclined to the axis of said gauge button, whereby said tapered side of said major conical portion is free from substantial contact with the wall of the bore hole.
 12. In a percussion bit as defined in claim 11; the axis of said gauge button being inclined to the axis of said body at an angle of from about 30* to 40*, the tapered side of said major conical portion of said gauge button being inclined to the axis of said gauge button at an angle of from about 25* to 35*. 